1. Field of the Invention
This invention relates to an optical system for photographing a stereoscopic image and a zoom lens suitable therefor, and an image pickup optical system provided with quantity-of-light controlling means for controlling the quantity of transmitted light by the utilization of polarization.
To observe a stereoscopic image, a plurality of parallax images become necessary. An optical apparatus for photographing a stereoscopic image and a photographing optical system for obtaining a plurality of parallax images are proposed, for example, in Japanese Patent Application Laid-Open No. 8-251624, Japanese Patent Application Laid-Open No. 8-307904, etc.
In FIG. 1 of Japanese Patent Application Laid-Open No. 8-251624, a stereoscopic image photographing optical system is comprised of two right and left variable reflection angle mirrors, two right and left mirrors, two sets of two right and left polarizing filters, two right and left lens systems and an image pickup element. The polarizing filters are rotated to thereby vary the quantity of light based on right and left parallax images, and lights passed through optical paths for right and left parallax images are alternately directed to the image pickup element to thereby obtain parallax images.
Also, in the embodiment of FIG. 2 of Japanese Patent Application Laid-Open No. 8-251624, a stereoscopic image photographing optical system is comprised of two right and left variable reflection angle mirrors, two right and left mirrors, a polarizing beam splitter, a polarizing filter, a lens system and an image pickup element. As in FIG. 1, the polarizing filter is rotated to thereby vary the quantity of light based on right and left parallax images, and lights passed through optical paths for the right and left parallax images are alternately directed to the image pickup element to thereby obtain parallax images.
On the other hand, in Japanese Patent Application Laid-Open No. 8-307904, a stereoscopic image photographing optical system is comprised of two right and left objective lenses, two right and left shutters, a half mirror for coupling two right and left images together, and a variable power optical system for re-imaging the primary imaging planes of the two right and left objective lenses on an image pickup element.
However, the stereoscopic image photographing optical system disclosed in the embodiment of FIG. 1 of Japanese Patent Application Laid-Open No. 8-251624 forms an image with the optical axes of two photo-taking lenses inclined with respect to the image pickup elements, and this has led to the disadvantage that the peripheral portion of the image field becomes blurred.
Also, in the stereoscopic image photographing optical system disclosed in the embodiment of FIG. 2 of Japanese Patent Application Laid-Open No. 8-251624, a polarizing beam splitter comprised of multilayer film is used as an optical path combining element for combining two optical paths. Therefore, there have been disadvantages that the characteristic of spectral reflectance is changed by a change in the angle of incidence of the light beam and that color irregularity occurs in the image field.
Also, as the quantity-of-light controlling means, a polarizing filter plate is used for the control of the transmission and non-transmission of a light beam and therefore, the light after being passed through the quantity-of-light controlling means (shutter) becomes polarized light. Therefore, in an image pickup apparatus using an image pickup element such as a CCD for periodically introducing an image as image pickup means, if a low-pass filter using double refraction is used, there has been the problem that the low-pass effect weakens and black and white moire and color moire occur and the picked-up image becomes unsightly.
Also, the photo-taking light is polarized by a polarizing plate disposed at the object side of the quantity-of-light controlling means, and this also has led to the problem that the luster of the object when a photographer actually sees with the naked eye and the luster of the picked-up image of the object differ remarkably from each other.
On the other hand, in Japanese Patent Application Laid-Open No. 8-307904, the aerial images of the two right and left objective lenses are re-imaged by a relay lens and therefore, the number of lenses constituting the entire optical system becomes great, and this has led to the disadvantage that the construction of the entire apparatus becomes complicated.
It is an object of the present invention to provide a stereoscopic image photographing optical system in which an optical system for photographing a plurality of parallax images is appropriately set, whereby optical performance is good and color irregularity is not created and a good stereoscopic image (parallax image) can be obtained easily, and a zoom lens suitable therefor.
It is another object of the present invention to provide an image pickup optical system in which when polarization is used to control the quantity of passed light and form the image of an object on an image pickup element such as a CCD, black and white moire and color moire occur little and an image in which the luster of an object becomes natural can be obtained easily, and a stereoscopic image photographing optical system using the same.
The optical system of the present invention is characterized by the provision of:
a pair of forward optical components each having a shutter for controlling the amount of transmission of a light from an object;
an optical member for laying the optical axes of said pair of forward optical components one upon the other; and
a rearward optical component disposed so that the optical axis thereof may coincide with said optical axes laid one upon the other;
said optical system alternately varying the amounts of transmission of the light transmitted through the shutters of said pair of forward optical components to thereby time-serially form a parallax image.
Also, the zoom lens of the present invention is characterized by the provision, in succession from the object side, of:
a first lens unit of negative refractive power;
a stop;
a second lens unit; and
at least two lens units of positive refractive power movable from the image plane side toward the object side independently of each other during the focal length change from the wide angle end (maximum wide-angle state) to the telephoto end (maximum telephoto state), said at least two lens units of positive refractive power having a meniscus negative lens convex toward the image plane side on the side most adjacent to the object.
Also, the zoom lens of the present invention from another point of view is characterized by the provision, in succession from the object side, of:
a first lens unit of negative refractive power fixed during focal length change;
a stop fixed during the focal length change;
a second lens unit; and
at least two lens units of positive refractive power movable from the image plane side toward the object side independently of each other during the focal length change from the wide angle end to the telephoto end.
Also, the image pickup optical system of the present invention is characterized by the provision of:
quantity-of-light controlling means for controlling the amount of transmission of light by the utilization of polarization;
an image pickup lens for forming an image by the use of the light transmitted through said quantity-of-light controlling means; and
a quarter wavelength plate disposed on at least one of the object side and the image plane side of said quantity-of-light controlling means.
Also, the image pickup apparatus of the present invention is characterized by the provision of:
quantity-of-light controlling means for controlling the amount of transmission of light by the utilization of polarization;
an image pickup lens for forming an image by the use of the light transmitted through said quantity-of-light controlling means;
an optical low-pass filter utilizing double refraction;
an image pickup element for periodically introducing the image thereinto; and
a quarter wavelength plate disposed on at least one of the object side and the image plane side of said quantity-of-light controlling means.